In-situ laser Raman scattering and far infrared spectroscopy studies of corrosion-passivation phenomena in metals.

Vibrational spectroscopic and electrochemical techniques are among the most useful tools for the elucidation of corrosion-passivation phenomena in metals. The former can provide information on the structure and composition of corrosion films ''in situ'' in aqueous solution environments, while thermodynamic and kinetic information may be obtained using electrochemical techniques. In this paper, we demonstrate the application of Laser Raman Scattering (LRS) and Synchrotrons Far Infrared Reflectance Spectroscopy (SFIRS), coupled with electrochemical methods, for the determination of the structure and composition of surface films on nickel and copper in aqueous solution environment. The corrosion film on nickel has been found to consist of NiO and Ni(OH){sub 2} in the passive region of potential and NiOOH in the transpassive region. The film on copper consists of Cu{sub 2}O, CUO and Cu(OH){sub 2}. We also show for the first time that SFIRS can be used to obtain information on the adsorption of ions on a metal surface with sub-monolayer sensitivity. Adsorption of Cl{sup {minus}}, Br{sup {minus}}, SO{sup {minus}2}, and PO{sub 4}{sup {minus}3} was found to occur at gold electrodes in perchloric acid solution. We also observed that when two different ions are present in solution, the more strongly adsorbed ion determined the corrosion behavior of the metal